Warm white light-emitting diode and thin film and its red phosphor powder

ABSTRACT

The invention discloses a red phosphor powder which is based on strontium (Sr) aluminate and using europium (Eu) as exciting agent, and is characterized by that its chemical equivalence formula is (SrO)4(ΣMe+2O)1Al2O3: Eu, wherein Me+2=Mg and/or Ca and/or Ba. The present invention also discloses a manufacturing process for the red phosphor powder and a warm white light-emitting diode employing the phosphor powder. Moreover, the present invention also discloses a multi-layer polyethylene thin film using the red phosphor powder.

FIELD OF THE INVENTION

The present invention relates to the field of microelectronics, and inparticular to a red phosphor powder related to the modern technologyfield broadly called solid state lighting and a warm whitelight-emitting diode employing the phosphor powder.

BACKGROUND OF THE INVENTION

With the technology foundation of the solid state lighting, somelighting facilities have been produced for daily and landscape uses aswell as high power lighting facilities for industrial uses. Theselighting facilities have a somewhat lower color temperature, T≦3500K,falling into the category of warm white lighting. If the colortemperature is higher, T>4600K, the semiconductor facilities will becategorized as cold white light.

The first red phosphor powder is a Lepard phosphor powder with a formulaof Me^(II)S:Eu⁺², wherein Me^(II) is equal to Ca⁺², Sr⁺², or Ba⁺². Thesecond type of phosphor powder is the compound of A^(II)B^(IV) whereinA^(II)=Zn, Cd and B^(IV)=S, Se, Te or their inter-soluble compounds, forexample, (ZnS)_(0.4)(CdS)_(0.6). Ag. The application of these phosphorpowders are now very limited because (1) Me^(II) S sulphide is low inchemical stability and readily decomposed in air, and (2) A^(II)B^(IV)compound contains cadmium, which is a strong toxin.

In 1965, the first rare earth phosphor powder was developed with avanadic acid, (Y,Eu)₁VO₄, as its substrate (please refer to Handbook ofPhosphors Press NY, 1999). The red phosphor powder has been produced inbatches. The excited wavelength of the near ultraviolet of the phosphorpowder is λ=365 nm. Since the phosphor powder has a good quality andhigh performance, it has been widely applied.

It was followed by the development of oxide phosphor powder: Y₂O₃:Eu orGd₂O₃:Eu, with an excited ultraviolet wavelength of λ=254 nm. Since thestability and performance of the phosphor powder are very high, it isstill now used in the light sources with η=50 lumen/watt. Later, theinvention of sulphur oxide phosphor powder with a formula of (ΣLn)₂O₂S,wherein ΣLn=Y, La, Gd, Eu, Tb, Sm. Based on the sulfur oxide phosphorpowder, new cathode phosphor powder, X-ray phosphor powder, and laserphosphor powder were invented (please refer to the Russian Patent No.1603763 by N. P. Soschin et al., Dec. 1, 1988). Although widely used,the red phosphor powder based on Yttrium (Y)-Lanthanum (La)-Gadolinium(Gd)-Europium (Eu) sulfide has a substantive drawback: the red lightwith wavelength λ=616, 626, and 708 nm can only be excited to luminesceat the near-ultra violet subband of wavelength λ=365˜405 nm. Therefore,the phosphor powder can only be applied in the semiconductor lightsource of λ=395 nm, and not suitable to be excited by the blue-lightsemiconductor heterojunction. The drawbacks of this phosphor powderbased on (Y,Eu)₂O₂S has been described in the Russian Patent No. 2064482please refer to the Russian Patent No. 2064482 by N. P. Soschin et al.,Apr. 18, 1991).

People later tried to develop phosphor powder which can be excited byblue light heterojunction to emit red light. A series of articlesconcerning the new oxide phosphor powder, CaSiAlN₃:Ce (please refer toHanz Luo Jiang et al and Materials Science and Engineering MSB 115118)details these experiments taken. However, the production of materialCaSiAlN₃:Ce is very complicated because of its low light output and highcost.

The present inventors of the present invention have recently attemptedto make the phosphor powder Sr₅Al₂O₈:Eu⁺³ disclosed in a newly publishedpatent as sample (please refer to N. P. Soschin, high-powder white lightsemiconductor). Nevertheless, the inventors of the patent did notclarify the exact composition of the phosphor powder when detailing thesynthetic process, nor specify the realizable oxidation state of themain exciting agent Eu⁺³. Also, the inventors did not specify thecrystal structure of the compound and the concentration ratio of SrO andAl₂O₃, which are drawbacks demanding improvement.

SUMMARY OF THE INVENTION

To overcome the prior drawbacks described above, the main objective ofthe present invention is to provide a red phosphor powder and warm whiteLight-emitting diode employing the phosphor powder capable of overcomingthe aforementioned drawbacks.

To overcome the prior drawbacks described above, another objective ofthe present invention is to provide a red phosphor powder and method ofmanufacturing it. A synthetic process is employed to produce thephosphor powder, which is excited by short-wavelength light;ultraviolet, violet, blue, pale blue, and blue-green; and emitsbroadband red light in the wavelength λ=600˜650 nm.

To overcome the prior drawbacks described above, another objective ofthe present invention is to provide a phosphor powder of high quantumyield and high performance.

To overcome the prior drawbacks described above, another objective ofthe present invention is to provide a super-fine phosphor powder with aparticle size reaching 1˜1.5 μm, which has two potential applications:warm white light-emitting diode and greenhouse light conversionagricultural film.

To achieve the aforementioned objectives of the present invention, a redphosphor powder according to the present invention is based on strontium(Sr) aluminate and uses europium (Eu) as exciting agent, and ischaracterized by that its chemical equivalence formula:(SrO)₄(ΣMe⁺²O)₁Al₂O₃: Eu, wherein Me⁺²=Mg and/or Ca and/or Ba.

The present invention also discloses a manufacturing process for the redphosphor powder and a warm white light-emitting diode employing thephosphor powder. Moreover, the present invention also discloses amulti-layer polyethylene using the red phosphor powder.

To achieve the aforementioned objectives of the present invention, awarm white phosphor powder according to the present invention has anIn—Ga—N heterojunction as its substrate and the surface of the In—Ga—Nheterojunction is covered with phosphor powder based on yttrium aluminumgarnet, which is characterized by that the yttrium aluminum garnet isadded with the aforementioned red phosphor powder.

To achieve the aforementioned objectives of the present invention, athin, multi-layer polyethylene film is used in a greenhouse or warmhouse. The thin, multi-layer polyethylene film is based on high densitypolyethylene and its derivative contains inorganic phosphor powder andis characterized by the film using the aforementioned red phosphorpowder as its constituent.

DETAILED DESCRIPTION OF THE INVENTION

First of all, the objective of the present invention is to overcome thedrawbacks of the aforementioned phosphor powder and the warm whitelight-emitting diode employing the phosphor powder. To achieve theobjective, the red phosphor powder according to the present invention isbased on strontium (Sr) aluminate and uses europium (Eu) as an excitingagent, and is characterized by that its chemical equivalence formula is(SrO)₄(ΣMe⁺²O)₁Al₂O₃: Eu, wherein Me⁺²=Mg and/or Ca and/or Ba; whereinthe exciting agent europium has two different oxidation states Eu⁺² andEu⁺³; the ionic ratio of the different states of the exciting agenteuropium is [Eu⁺²]/[Eu⁺³]=1:10˜1:1; the concentrations of the mainanions of group II A are as follows: Mg⁺² from about 0.025 to about0.90, Ca⁺² from about 0.001 to about 0.50, and Ba⁺2 from about 0.001 toabout 0.50, and wherein the sum of the concentrations or atomicfractions is equal to 1 (Mg+Ca+Ba=1; the maximum of the excitationspectrum of the phosphor powder is in the range of 390≦λ≦550 nm, and themaximum of the excitation spectrum is related to the charge transfer inthe band: charge transfer occurring between Eu⁺³ and O⁻² and thusforming a charge coalescence Eu⁺²+O⁻¹; and the phosphor powder excitedby short wavelength radiation, shorter than 460 nm, emits in theorange-red zone, λ>585 nm.

The physical chemistry principle of the phosphor powder according to thepresent invention is outlined hereinafter. First, a new compositionframework of the phosphor powder according to the present invention isdeveloped to replace (SrO)₅Al₂O₃, which cannot be manufactured easily:SrO being replaced with a combination of metallic oxides,ΣMe⁺²O=aMgO+bCaO+cBaO, wherein a+b+c=1.

Without destroying the overall charge balance of the crystal lattice ofthe phosphor powder, the crystal lattice framework of the phosphorpowder has been developed to control the performance of the phosphorpowder: brightness, color ratio, particles size, for example. Theframework according to the present invention includes all oxides ofgroup HA for all elements in the periodic table except SrO. It is knownthat the ionic radius of metal elements with +2 oxidation state aredifferent; the ionic radius of Mg⁺² is τ_(Mg)=0.58A; that of Ca⁺²,τ_(Ca)=1.05 A; and that of Ba⁺², τ_(Ba)=1.20A. When different amounts ofthese elements are added into the phosphor powder containing group HAelements, the average radius of group HA ions can approach that of Sr⁺²ions (τ_(Sr)=1.16 A). However, the solubility of Eu⁺² ions at latticepoints increases with larger concentration of larger ions, Ca⁺² andBa⁺². If a larger amount of Mg⁺² is found in the crystal lattice, theamount of reactive ions Eu⁺² will be decreased.

It is also considered that the compounds according to the presentinvention are produced from strontium spinel SrAl₂O₄. After the majorperformances are (slightly) changed, additional SrO or MeO oxides addedwill enter the main crystal lattice of spinel (and combine with theorthorhombic lattice phase).

From the following evidences, it can be proved that the major excitingagent has two oxidation states: (1) The excitation spectrum of thephosphor powder is a broadband emission, which is close to the spectrumof the (Ca, Sr)₂SiO₄:Eu⁺² in term of structure. Also, the oxidationstate of Eu in the compound is exactly Eu⁺² and the excitation spectrumof the compound is very broad with an excited wavelength of λ=365˜475nm. (2) In the phosphor powder model proposed according to the presentinvention, the emission spectrum of the exciting agent (Eu⁺²) falls intothe category of broadband emission: λ_(0.5)>30˜40 nm, instead of narrowband emission. It is widely known that the half bandwidth of theemission spectrum of Eu⁺³ is λ_(0.5)=5˜6 nm, which does not change muchwhen migrating to different crystal lattices. (3) The luminescence ofτ=2.5 nano-seconds are because part of Eu⁺³ ions to be located in Al⁺³(in this crystal lattice, there exists Dy⁺³ ions of 3-valance state,which forms reactive pairs in the (SrAl₂O₄:Eu⁺²Dy⁺³ phosphor powder.).

The present invention discloses that a charge-transfer group forms inthe phosphor powder according to the present invention. Thecharge-transfer group consists of the following constituents: Eu_(Sr)⁺²+O_(O) ⁻+Eu_(Al) ⁺³. Each constituent in the charge-transfer group hasits own distinct function: Eu⁺² ions form a broad excitation spectrum;Eu⁺³ ions impose the narrow band emission of Eu⁺³ into the broadbandemission of Eu⁺² (the broad band is a distinct feature of CaS:Eu orSrS:Eu phosphor powder); oxygen ions exert their function in the chargetransfer by changing oxidation state; an O⁻² ion gives away an electronto become O⁻¹, which becomes a charging ion charging Eu⁺³ ion by passingan electron (e) to it. According to Eu⁺³+O⁻²(ē)+O⁻¹, Eu⁺³ ions receivean electron to return to its initial condition. Then, it is thewell-known reaction: Eu⁺²+O⁻¹+Eu⁺²→E⁺³*+O⁻²*+Eu²⁺. The excited Eu⁺³ ionswill definitely emit and at the same time Eu⁺² will do so. If Eu⁺³ ionsgive narrow band emission, then Eu⁺² ions give broad band emission, ofwhich maximum radiation may be located at the green SrAl₂O₄:Eu band,yellow-green (Sr,Ba)₂SiO₄:Eu band, and red CaS:Eu band of the spectrum.

Consequently, the phosphor powder according to the present invention ischaracterized by its two emission centers, which belong to the sameactive ion, the europium ion. If electron paramagnetic resonance is notundertaken, it is difficult to determine the number and ratio of eachactive emission center. However, the half bandwidth of the spectrumcurve proposed in the present invention can be employed to determinethese values. The underlying principle of the method is to compare thehalf bandwidth of the spectrums of the compounds; for example, when themaximum wavelength is λ=616 nm, the half bandwidth of Al₂O₃:Eu⁺³λ_(0.5)=5 nm; when the maximum wavelength is λ=650 nm, the halfbandwidth of SrS:Eu⁺² is λ_(0.5)>85 nm; when the maximum wavelength isλ=640 nm, the half bandwidth of the sample (SrO)₄(Mg,Ca,Ba)₁OAl₂O₃synthesized according to the present invention is λ_(0.5)=45 nm. As forthe decrease of the half bandwidth, it is possible only related to thesecond emission center Eu⁺³. Nevertheless, the simplest ratio(85−45)/85≈55% suggests that Eu⁺² and Eu⁺³ are equal in the phosphorpowder according to the present invention. On the other hand, thephosphor powder according to the present invention has a half bandwidthof λ_(0.5)=80 nm, indicating that Eu⁺² has a value approaching 90% inthe two-valence ions of the phosphor powder. Another advantage of thephosphor powder according to the present invention, the half bandwidthand maximum location of the emission band can be changed.

The condition to realize this important characteristic of the redphosphor powder is that the major group IIA anionic ions in the phosphorpowder include: Mg from about 0.25 to about 0.90, Ca from about 0.001 toabout 0.50, and Ba from about 0.01 to about 0.50, wherein the sum of theatomic fractions is equal to 1 (Mg⁺ Ca+Ba=1). The analysis for the roleof the Alkali earth metals in the phosphor powder indicates that thelargest Ba⁺² ions entering Me⁺² group will induce the shortwave shift ofradiation: from red to orange with a shift of Δ≦10 μm, which issufficient to change the luminescence purity and reduce color saturationof red light. On the other hand, Mg⁺² ions have a negligible effect onthe spectrum structure, but have a strong effect on luminescentintensity. With the addition of a large amount of Mg⁺² ions, thebrightness of the phosphor powder will be enhanced accordingly. When theconcentration of magnesium is [Mg]=0.8 atomic fraction, the brightnessof the phosphor powder increases by 25%. Another important function ofthe addition of Mg⁺² ions is to reduce the particles size of thephosphor powder. When the concentration of magnesium increases fromabout 0.25 to about 0.9 atomic fraction, the particles size of thephosphor powder is reduced from d₅₀=0.8 μm to d₅₀=0.5 μm.

The concentration of Ca⁺² in the phosphor powder will also change thecrystal lattice of the compounds of the phosphor powder. When [Ca]≈0atomic fraction, the crystal is an orthorhombic lattice; when [Ca]=0.50atomic fraction, the crystal is a monoclinic crystal lattice. Also, theshape of the natural radiation spectrum will be changed as a result; thenumber of maximum value (peak) in the radiation spectrum will changefrom two to three or even four. When a large amount of Ca⁺² is added, along wavelength shift of Δ=12 μm will occur. The aforementioneddescription explains the substantial change of crystal lattice in theMe⁺²O phosphor powder.

The maximum in the excitation spectrum of the red phosphor powder occursat the wavelength of λ=390˜50 nm, which is probably related to thecharge transfer between Eu⁺³ and O⁻² ions and the formation of Eu⁺²+O⁻¹valence group. The Eu⁺²+O⁻¹ valence group is located in the radiationzone of the In—Ga—N heterojunction, which is in the range of λ=450˜470nm.

The present invention has noted that the abnormal broadband excitationspectrum starts in the near ultraviolet zone and ends in the greensubband. As described earlier, the broadband excitation spectrum isprobably only related to the charge-transfer band, in which charges movefrom oxygen or SrO ions to europium ions. Another scenario is that thecharges of Eu⁺³ ions should move very fast because there are four oxygenions on the side of the excited ion. That the extended excitation zoneof the half wavelength larger than 120 μam suggests the effectiveness ofEu⁺² is very large—excited ions Eu⁺² have a stronger effect than thedata of SrAl₂O₄ in the phosphor powder, approaching that Eu⁺² of in CaS.

It has to point to that the integration of the phosphor powder withultraviolet heterojunction or violet, blue-pale blue radiator can leadto this kind of broadband excitation spectrum. It is promising to applythe phosphor powder in light conversion agricultural film because if thephosphor powder is used in light conversion agricultural film, all theexcitation energy accumulated in the ultraviolet and blue-green subbandswill be stored in the red zone of the spectrum, speeding up thephotosynthesis of green plants.

The main advantage of the red phosphor powder according to the presentinvention lies in the fact that the phosphor powder is excited byshort-wavelength (less than 460 μm) light and emits light at theorange-red zone of wavelength λ>585 nm. The following description willsummarize the advantages of the phosphor powder: Today's whitelight-emitting diodes generally have a maximum radiation spectrum atλ=575 nm (Gd₃Al₅O₁₂:Ce). Although some other oxides and nitrous oxideshave a higher wavelength, their quantum output of radiation is not high.On the other hand, the phosphor powder according to the presentinvention has a red radiation spectrum of very high wavelength, and thusis suitable to be used in the making of white light-emitting diode. Thephosphor powder may be used together with yttrium-aluminium (YAG), forexample Y₃Al₅O₁₂:Ce, Tb₃Al₅O₁₂:Ce, (Lu,Tb,Y)₃Al₅O₁₂:Ce, and(Sr,Ba)₂O₄:Eu.

The following description will stress the synthesis characteristics ofthe red phosphor powder according to the present invention. There arethree synthesis processes to produce the phosphor powder: (1)high-temperature solid-phase synthesis; (2) sol-gel process, in whichphosphor powder particles undergo synthetic reaction in a liquid phase;and (3) micro-emulsion synthesis, in which micro-reaction phosphorpowder particles according to colloidal chemistry undergo chemicalreaction between particles.

The three methods have their respective advantages and disadvantages.High-temperature solid phase synthesis is very simple, but only at hightemperature many solid phases can be formed and high temperature willreduce the brightness of the phosphor powder. Sol-gel process takesplace at the temperature 300˜400° C., but secondary phases cannot beovercome; also, particles agglomeration occurs in the phosphor powderduring the sol-gel process and it takes time to fragment them.Micro-emulsion synthesis requires small particles of the phosphor powderand leads to a large amount of un-burned carbon impurities.

The aforementioned analysis points out that there is no common synthesisprocess to produce different compositions of phosphor powder, and it isprobably no such common process. Therefore, the first aim of the presentinvention is to develop a new synthesis for the red phosphor powderbased on strontium aluminate. The aforementioned description hasexplained the chemical composition of the red phosphor powder, of whichstrontium and aluminum oxides undergo mutual reactions during heating.The new synthesis process is characterized by Sr(OH)₂.8H₂O hydroxide,which is used as the original ingredients for the compounds ofstrontium-barium group and Mg(CH₃COO)₂.4H₂O and Ca(CH₃COO)₂.4H₂O acetatehydrates as the original ingredients for the compounds ofmagnesium-calcium group. The aluminum hydroxide Al(OH)₃ is used as thebasic compound of the phosphor powder and the initial amount ofhydroxide is higher than its stoichiometric value by preferably0.015˜0.11%. There are physical and chemical distinctions between thenew synthesis process and the existing elemental synthesis process forGroup II aluminate. First, the new synthesis process does not have thecarbonate elements of Group II, which are hard to be decomposed, forexample SrCO₃, CaCo₃, BaCo₃ or MgCO₃. Instead, the new synthesiscontains strontium and barium hydroxides, Sr(OH)₂.8H₂O and Ba(OH)₂.8H₂O,which can be decomposed at rather low temperature T≦400° C. and will notundergo phase transformation during heating. Similarly, acetatehydrates, Mg(CH₃COO)₂.4H₂O and Ca(CH₃COO)₂.4H₂O can decomposed at T<500°C. without leaving carbon remnants.

The following example shows new synthesis processes are used to obtainthe red phosphor powder according to the present invention.

Example 1

-   -   Prepare 0.4 M (mole)Sr(OH)₂.8H₂O,    -   0.05M Mg(CH₃COO)₂.4H₂O,    -   0.03 M Ca(CH₃COO)₂.2H₂O,    -   0.02 M Ba(OH)₂.8H₂O,    -   0.001M Eu₂O₃, and        2.02M Al(OH)₃ and put them into a planet ball mill for mixing at        a rotation speed ω=1000 rotation/minute. Then, the ingredient is        placed in a crucible of V=1000 ml, which is then heated in a        furnace, filled with preferably an atmosphere of 99% N₂ and 1%        CO. The furnace is heated to T=950° C. in 5° C./minute up and        kept at the temperature for two hours. The ingredient is then        removed from the crucible and cleaned with hot water, and is        ready for physical and chemical experiments. First, the chemical        composition of the ingredient is consistent with the chemical        formula, (SrO)₄[(Mg,Ca,Ba)O]₁Al₂O₃, with a color of pale yellow,        and it is easily dispersed in water. The phosphor powder excited        by the blue light from light-emitting diodes emits strong        orange-red light, of which chromaticity coordinate is x=0.645        and y=0.343. The brightness of the phosphor powder excited by        the blue light from light-emitting diodes exceeds that of        CaSEuLi phosphor powder. The average particles size of the        phosphor powder according to the present invention is d_(cp)≦2.1        mm.

The excellent luminescence as well as physical and chemical parametersensure the ingredient of the red phosphor powder can be added with 0.05%to 0.1% mole of Al(OH)₃ hydroxide remnant.

It is found that the aluminate hydroxide remnant is indispensable forthe phosphor powder to form liquid drops or linear structure. If theaddition of Al(OH)₃ hydroxide into the ingredient of the red phosphorpowder is insufficient, the phosphor powder particles are nano-meterparticles that will form the shape of flakes or a squamous structure ofwhich the average particle size, d_(cp), is 0.5-0.8 μm.

It is also found that the oxidation state of active Eu ions isdetermined by the heating period and each cycle's heating temperature ofthe ingredient. Two-stage calcining can obtain redder phosphor powder;the first stage is low-temperature calcining, from 150° C. to 200° C.,and the second stage is from 950° C. to 1100° C. The furnace during theentire heating process is filled with weak-reduction atmosphere, whichis preferably a mixture of 99% N₂ and 1% CO. While this mixture ispreferred, several satisfactory mixtures would be sufficient, includingmixtures with a CO content of 0.05 (5%) or less. The above process canproduce the phosphor powder with a small particles size, of which themaximum particle size is d₅₀≈500 nm and the particles larger than 4 μmis less than 5%.

The following description will be focused on the applicationcharacteristic of the red phosphor powder. First, the characteristiccomes from the properties of the phosphor powder (described earlier)according to the present invention, i.e. its excitation spectrum,regardless of blue, pale blue, or even pale blue-green zone, having abroad subband. The unique characteristics of the red phosphor powder canbe applied in two specific areas: (1) the ingredient of light-emittingdiodes with red subband, and (2) the filler of multi-layer polyethyleneused in greenhouse and warm house.

The present invention has conducted related experiments for theapplication of the phosphor powder according to the present invention indouble-layer white light-emitting diodes. Light-emitting diodes can beobtained with In—Ga—N heterojunction, which has a blue light wavelengthof λ=460 nm in the spectrum. The radiation surface of the heterojunctionis covered with suspending liquid based on organic silicon and theyellow phosphor powder based on yttrium aluminum garnet,(Y,Gd)₃Al₅O₁₂:Ce. If the suspending liquid is added with theaforementioned phosphor powder with the composition of(SrO)₄[(Mg,Ca,Ba)O]Al₂O₄:Eu^(+2,3), the radiation of the light-emittingdiodes can be shifted additionally toward warm red zone. Moreover, theshift of the radiation color temperature of light-emitting diodes isdetermined by the parameters of the red phosphor powder. All thelighting parameters of the phosphor powder are listed in TABLE 1.

TABLE 1 Color Luminesce Temperature Intensity Chromaticity of light(mcd) Coordinates Relative emitting under No. Chemical Compositions x yLuminescence % diode, K 30 mA 1(SrO)₄(Mg_(0.5)Ca_(0.3)Ba_(0.2)O)Al₂O₃:Eu 0.645 0.343 122 3100 4500 2(SrO)₄(Mg_(0.6)Ca_(0.2)Ba_(0.2)O)Al₂O₃:Eu 0.650 0.340 116 3000 3950 3(SrO)₄(Mg_(0.9)Ca_(0.05)Ba_(0.05)O)Al₂O₃:Eu 0.655 0.338 112 2940 3800 4(SrO)₄(Mg_(0.45)Ca_(0.45)Ba_(0.1)O)Al₂O₃:Eu 0.642 0.350 128 3190 5000 5(SrO)₄(Mg_(0.4)Ca_(0.5)Ba_(0.1)O)Al₂O₃:Eu 0.638 0.354 136 3280 6000 6Standard Sample 120 4500 6500 1 Remark: The mixture of the phosphorpowder is used in the warm white light-emitting diodes andlight-emitting diodes made with the mass ratio 20:80 of the red phosphorpowder and yttrium aluminum garnet is preferable and can emit veryuniform warm white light.

TABLE 1 indicates that the radiation color temperature of thelight-emitting diodes can be lower than 4500K (the color temperature oflight-emitting diodes can be as low as T=2940K, similar to that of theradiation of filament lamps, T=2850K). The luminescent color(chromaticity coordinate) and even the luminous intensity of thephosphor powder are substantially enhanced. The luminous intensity ofthe phosphor powder is very high, I=6000 mcd and 2θ=60°. The luminousintensity of the warm white light-emitting diodes reaches such a highvalue is rarely seen in the world.

Light conversion agricultural film is another application of the redphosphor powder according to the present invention. The study for thisapplication direction is very active in today's agricultural biologyresearch. Existing studies indicate that agricultural films filled withred phosphor powder can have 1.25˜1.8 times of yields of various cropscultivated in greenhouses and warm houses. The phosphor powder excitedby the ultraviolet in the sunlight emits red light to crops, therebyenhancing the photosynthesis of green plants. Also, with the phosphorpowder, the rich vitamin C contained in vegetables and fruits can beincreased to about three times.

The micro-sized particles of the red phosphor powder can be applied ontoa single layer or multi-layer polyethylene thin films. The phosphorpowder used in many patents (refer to U.S. Pat. No. 6,153,665, Nov. 28,2000, by N. Soschin et al.; Malaysian Patent MY PA 01004165A,26.04.2001; and Canadian patent) is sulphur-oxide, Ln₂O₂S:Eu. However,the present invention has found that similar photo biological reactioncan only occur when polymer films are filled with the red phosphorpowder according to the present invention. When the red phosphor powderis added into agricultural films, the optimum mass concentration is0.1˜1.5%.

In summary, the light-emitting diodes according to the present inventionhas a uniform luminescence color, a warm white emission, a chromaticitycoordinate of 0.41≦x≦0345 and 0.40<y≦0.43, and a color temperature of2800≦T≦3400K. Also, the light-emitting diodes according to the presentinvention can create a light source of higher brightness and largerluminous flux, and can indeed overcome the drawbacks of conventionalwarm white light-emitting diodes.

It is appreciated that although the directional practice device of thepresent invention is used in a very limited space instead of practicingat the real playing field, effective and steady practice can be obtainedas well. Further, it is very easy to set up and to operate thedirectional practice device of the present invention. These advantagesare not possible to achieve with the prior art.

While the invention has been described with reference to the a preferredembodiment thereof, it is to be understood that modifications orvariations may be easily made without departing from the spirit of thisinvention, which is defined by the appended claims.

1. A red phosphor powder based on strontium aluminate, using europium(Eu) as an exciting agent, and characterized by that its chemicalequivalence formula is (SrO)₄(ΣMe⁺²O)₁Al₂O₃: Eu, wherein Me⁺² is Mg, Ca,Ba, and mixtures thereof.
 2. The red phosphor powder as defined in claim1, wherein the exciting agent europium has two different oxidationstates, Eu⁺² and Eu⁺³.
 3. The red phosphor powder as defined in claim 2,wherein the ionic ratio of the different states of the exciting agenteuropium is [Eu⁺²]/[Eu⁺³]=1:10˜1:1.
 4. The red phosphor powder asdefined in claim 1, wherein the concentrations of Mg, Ca, and Ba are Mgfrom about 0.025 to about 0.90, Ca from about 0.001 to about 0.5, Bafrom about 0.001 to about 0.5, and Mg+Ca+Ba=1.
 5. The red phosphorpowder as defined in claim 1, wherein the maximum in the excitationspectrum of the red phosphor powder occurs at the wavelength ofλ=390˜550 nm, in which the maximum is related to the charge transferbetween Eu⁺³ and O⁻² ions and the formation of Eu⁺²+O⁻¹ valence group.6. The red phosphor powder as defined in claim 1, wherein the phosphorpowder excited by short wavelength radiation, shorter than 460 nm, emitsin the orange-red zone, λ>585 nm.
 7. A warm white light-emitting diode,wherein the warm white light-emitting diode uses In—Ga—N heterojunctionas its substrate and the surface of the In—Ga—N heterojunction iscovered with a phosphor powder based on yttrium aluminum garnet, whichis characterized by that the yttrium aluminum garnet is admixed with thered phosphor powder defined in claim
 1. 8. A warm white light-emittingdiode as defined in claim 7, wherein the mass concentration of the redphosphor powder is 20%.
 9. A multi-layer polyethylene thin film for usein greenhouse or warm house based on high density polyethylene and itsderivative, which contains inorganic phosphor powder, the thin filmbeing characterized by that it contains the red phosphor powder asdefined in claim
 1. 10. A multi-layer polyethylene thin film as definedin claim 9, wherein the amount of the red phosphor powder added is about0.1˜1.5% in mass concentration of the polymer and phosphor powdermixture.